When a work is machined using laser light (hereinafter, laser machining), the focal position, which is the focal point of the laser light, is to be determined as accurately as possible. This is because the energy density of the laser light is highest at the focal position where machining such as cutting and welding is most efficiently performed. Therefore, in laser machining, the focal length of laser light, which depends on the type of the optical system such as a condenser lens, is to be kept constant. If the focal length of laser light is not constant, the work is irradiated with laser light with varying energy density. As a result, laser machining is performed in unstable conditions, resulting in poor machining performance. To achieve satisfactory machining performance, not only the focal length of the laser light but also the distance between the laser machining head and the work (the work distance) are to be kept constant.
In laser machining, the radiation angle of the laser light with respect to a work is to be determined as accurately as possible. For example, in the case of laser welding, improper radiation angles of the laser light result in a shallow depth of weld penetration into the work, causing the machined work to have insufficient strength. The preferable radiation angle of the laser light with respect to a work is within ±10° from the direction perpendicular to the surface of the work to be machined.
For these reasons, the work distance and the radiation angle of the laser light have been set as optimal as possible.
Patent Literature 1 discloses a laser machine in which a three-axis positioner controls the posture of an object to be machined in such a manner that the surface of the object to be machined is perpendicular to the laser light.
Patent Literature 2 discloses a laser welding device in which the beam from one laser oscillator is distributed to a plurality of welders. The device of Patent Literature 2 will now be described with reference to FIG. 7. As shown in FIG. 7, according to the conventional laser welding device, select mirrors 103, 104, and 105, which can be moved back and forth by select mirror drive means 106, 107, and 108, respectively, are provided on the optical axis of beam 102 emitted from laser oscillator 101. Select mirror drive means 106 to 108 are coupled with select mirror controller 113. Controller 113 controls these means 106 to 108 in accordance with operating condition signals 109, 110, 111, and 112, received from welders A to D (not shown).
As shown in FIG. 7, when the beam is led to welder B, select mirror controller 113 drives select mirror drive means 107 to put select mirror 104 on the optical axis of beam 102. As a result, beam 102 is reflected by select mirror 104 and led to welder B. Similarly, when beam 102 is led to welder A, select mirror controller 113 drives select mirror drive means 106 to put select mirror 103 on the optical axis of beam 102. When beam 102 is led to welder C, select mirror controller 113 drives select mirror drive means 108 to put select mirror 105 on the optical axis of beam 102. When beam 102 is led to welder D, select mirror controller 113 does not drive select mirror drive means 106 to 108 so that beam 102 is led straight to welder D.
As described above, beam 102 of laser oscillator 101 is distributed to welders A to D, allowing laser oscillator 101 to occupy a small area in the laser welding device. In welders A to D, those waiting for the index to arrive are skipped, and the others in use for welding can sequentially receive beam 102 from laser oscillator 101. This makes the best use of the entire energy of single laser oscillator 101. Furthermore, select mirrors 103 to 105 can be moved without changing their angles of reflection, so that the stopping accuracy of these mirrors 103 to 105 is not influential at the time of selecting them.